Thomas Heeney was born at Kaiti, Gisborne, on 18 May 1898, the ninth of ten children of Irish immigrants Hugh Heeney, a labourer, and his wife, Eliza Coughlan. He was educated in Gisborne at St Mary's and Te Hapara schools, and after working briefly for a blacksmith was apprenticed to a local plumber. He was to work in the plumbing trade until he left New Zealand in 1924.
Hugh Heeney taught his sons to box and two of them, Jack and Tom, showed unusual talent. Both were also representative rugby players, and Tom was a member of the Hawke's Bay–Poverty Bay team that played South Africa in 1921. He was also a powerful swimmer: in 1918 he was awarded a medal by the Royal Humane Society of New Zealand for his part in the rescue of two young women off Waikanae Beach. Jack Heeney was a New Zealand champion boxer at both amateur and professional level and he encouraged his younger brother to take part in amateur bouts, both of which he won.
Tom Heeney possessed a fine physique, standing 5 feet 10 inches tall and at his peak weighing 14 stone. He turned professional in 1920. After winning his first two bouts, he challenged Albert Pooley for the New Zealand heavyweight title in October that year, and won on a points decision. In 1922 he visited Australia, where he won five, lost two and drew two of his nine bouts. He relinquished his New Zealand title by going to Australia, but soon after returning home he regained it by stopping Brian McCleary in 14 rounds. He then lost to Jim Sullivan – his only defeat in New Zealand – but won the title back in a return bout.
In 1924 Tom Heeney left for Britain to further his boxing career. He suffered a poor start, losing on points to British champion Phil Scott in a one-sided contest. After a further three bouts Heeney visited South Africa where he won four of his five fights. On his return to Britain he beat Irish champion Bartley Madden in Dublin. This and other successes encouraged him to try his luck in the United States, and he sailed for New York in 1926.
A series of victories against prominent boxers gained Heeney number four ranking among the world's heavyweights. After taking part in an elimination series to find an opponent for world champion Gene Tunney, the New Zealander emerged with the best credentials. Popular with American crowds, he was known as 'The Hard Rock from Down Under' because of his non-stop style and his refusal to back away from an opponent. On 26 July 1928 Heeney, who remains the only New Zealand-born heavyweight to fight for the world championship, met Tunney in front of 46,000 spectators at Yankee Stadium, New York. He entered the ring wearing a Maori cloak sent to him by Sir James Carroll's widow, Heni Materoa. Guaranteed $100,000 for the bout, Heeney fought with great courage and did well in the early rounds, but he had little chance against the skilful Tunney; the bout was stopped in the 11th round to save him from further punishment.
A week later, on 2 August 1928, Heeney married Marion Estelle Dunn at Suffern in New York state. At the end of August the couple left on a visit to New Zealand, where there had been tremendous interest in Heeney's title bid. He and his wife were welcomed by huge crowds throughout the country, especially at his home town of Gisborne. On his return to the United States Heeney took out American citizenship and continued to box until 1933. Of his 69 professional bouts he won 37, lost 22 and drew 10.
During the Second World War Tom Heeney served in the United States Navy Civil Engineer Corps. He acted as a boxing instructor and refereed several armed forces bouts around the South Pacific. In 1947 he again visited New Zealand to see his mother and other family members. His boxing career had been financially rewarding, and for many years he owned a restaurant in Miami, Florida. Heeney made another brief visit to New Zealand shortly before his death, in Miami, on 16 June 1984. Marion had died in 1980; there were no children of the marriage.